Emulsion containing an oppositely-charged surfactant and polymer and the production method thereof

ABSTRACT

The present invention relates to an emulsion and to its manufacturing method. The emulsion is optimized in that it is stabilized by the presence of a surfactant specifically selected according to the type of a polymer, or copolymer, also present in the emulsion. The surfactant and the polymer are selected oppositely charged.

FIELD OF THE INVENTION

The present invention relates to an emulsion of at least two immisciblefluids, stabilized by an optimized combination of surfactants andpolymers, or of hydrosoluble copolymers. Preferably, the base fluids ofthe emulsion are oil and water.

The emulsions according to the present invention can be used in manyfields of application, for example the petroleum sphere, the cosmeticsindustry, the pharmaceutical industry, the food-processing industry,road surfacing, polymer synthesis, etc.

SUMMARY OF THE INVENTION

The present invention thus relates to an oil-in-water emulsioncomprising at least a surfactant and a polymer, the surfactant and thepolymer being selected oppositely charged.

The applicant has found that, surprisingly enough, it is possible tocontrol obtaining a stable or practically stable emulsion from acomposition of optimized surfactant concentration if a polymer or acopolymer oppositely charged in relation to the surfactant is associatedtherewith. A cationic polymer or copolymer is associated with an anionicsurfactant, and an anionic polymer or copolymer is associated with acationic surfactant.

It is possible to use as surfactants in the present invention all theconventional anionic surfactants, such that the anionic function is:

-   -   carboxylates:        -   alkaline metal soaps, alkyl or alkylether carboxylates,        -   N-acylaminoacids,        -   N-acylglutamates,        -   N-acylpolypeptides,    -   sulfonates:        -   alkylbenzene sulfonates,        -   paraffin sulfonates,        -   α-olefin sulfonates,        -   petroleum sulfonates,        -   lignosulfonates,        -   sulfosuccinic derivatives,        -   polynaphthylmethane sulfonates,        -   alkyltaurides,    -   sulfates:        -   alkyl sulfates,        -   alkylether sulfates,    -   phosphates:        -   monoalkyl phosphates,        -   dialkyl phosphates,    -   phosphonates.

The following cationic surfactants can be mentioned:

-   -   alkylamine salts,    -   quaternary ammonium salts whose nitrogen:        -   comprises a fatty chain, for example, alkyltrimethyl or            triethyl ammonium derivatives, alkyldimethyl benzylammonium            derivatives,        -   comprises two fatty chains,        -   is part of a heterocyclic structure, for example,            pyridinium, imidazolinium, quinolinium, piperidinium,            morpholinium derivatives.

All the conventional anionic polymers can be used according to thepresent invention, for example:

-   -   synthetic polymers or copolymers derived from:        -   anionic monomers containing carboxylate or sulfonate or            phosphate or phosphonate groups, such as acrylate,            methacrylate, itaconate, 2-acrylamido-2-methyl-propane            sulfonate, 2-methacryloyloxy ethane sulfonate,            3-acrylamido-3-methyl butanoate, styrene sulfonate, styrene            carboxylate, vinyl sulfonate monomers, maleic acid salts,    -   synthetic copolymers derived from:        -   anionic monomers, for example in those described above, and            neutral monomers, for example acrylamide, acrylic acid,            vinyl pyrrolidone, ethylene oxide, propylene oxide, maleic            anhydride, vinylic alcohol, hydroxyethylacrylate, . . .    -   natural polymers such as:        -   CMC type negatively modified cellulose derivatives,        -   polysaccharides of xanthan, alginate, arabic gum type,        -   negatively modified starches,        -   negatively modified galactomannanes.

All the conventional cationic polymers can be used according to thepresent invention, for example:

-   -   synthetic polymers or copolymers derived from conventional        cationic monomers, i.e. of the following general formula:        where R1 or R2 comprise at least one N atom.    -   polyethylene imines,    -   polyamide amines,    -   polyamines,    -   synthetic copolymers derived from:        -   cationic monomers and neutral monomers (described above).    -   natural polymers:        -   positively modified starches,        -   chitosanes,        -   gelatin,        -   positively modified galactomannanes,        -   positively modified cellulose derivatives.

According to the invention, the surfactant used can be cationic and havea concentration below approximately 5.10⁻³ mol/l, and the polymer can beanionic.

The surfactant can be anionic and have a concentration belowapproximately 5.10⁻³ mol/l, and the polymer can be cationic.

The anionic polymer can be an AM/AMPS type copolymer whose charged partproportion can range between 1 and 50%, preferably between 10 and 25%.The surfactant can be of DOTAB type.

The anionic polymer can be a copolymer of AM/acrylic acid type in analkaline medium whose acrylic acid proportion can range between 1 and50%, preferably between 10 and 25%. The surfactant can be of DOTAB type.

The anionic polymer can be a natural polymer, for example of arabic gumtype.

The cationic polymer can be a copolymer of AM/ADC type whose chargedpart proportion can range between 1 and 50%, preferably between 10 and25%. The surfactant can be of SDS type.

The invention also relates to a method for manufacturing an emulsion,from water and oil, of at least one surfactant and at least onehydrosoluble polymer. In the method, a surfactant and a polymer, or acopolymer, oppositely charged, are combined in the aqueous phase and thepolymer concentration is determined to obtain a stable emulsion with thelowest possible surfactant proportion below a 5.10⁻³ mol/lconcentration.

The polymer concentration can be determined as a function of the chargerate of the polymer and of the concentration in surfactant used.Considering the electrostatic nature of the interactions between polymerand surfactant, their respective concentrations can be a function of theionic strength of the medium.

The surfactant is thus rather and sufficiently water soluble so that,after mixing in the water with the hydrosoluble polymer, a complex formsand is set at the interfaces.

The emulsion can also contain solids (cuttings, neutral colloids, . . .) or other non-charged hydrosoluble polymers, anticorrosion additives,etc.

Other features and advantages of the present invention will be clearfrom reading the description of non limitative tests hereafter.

The tests are mainly based on the comparison, for different compositionsof emulsion additives (surfactants and polymers), of the emulsionstability measurement during bottle tests. Stability is evaluated bydetermining two half life times as defined below:

Procedure

The emulsions are prepared as follows. The surfactant at variableconcentration and the hydrosoluble polymer, also at variableconcentration, are incorporated to the aqueous phase. If necessary, thepH value is then adjusted by addition of acid or soda. Emulsification iscarried out at ambient temperature in a 200-ml beaker by means of aHeildoph stirrer provided with a three-paddle propeller. The rotatingspeed is generally 800 rpm. In general, the stirring time is about 20minutes. Addition of oil is carried out by means of a disposable syringein the aqueous solution. The ratio of the water/oil phases is variable.In the following examples, the ratio is of the order of 30 to 40% bylimitative, other proportions are suitable insofar as they can form anemulsion. In all of the examples described, the emulsions obtained areof oil-in-water type.

The bottle tests allow to monitor the behaviour of the emulsion formedin the course of time. The total volume of freshly manufactured emulsionis fed into a 100-ml test tube. The emulsion is then regularly observedso as to determine the kinetics of the separation phenomena. In oursystem, the various phenomena observed are:

-   -   emulsion creaming,    -   oil coalescence.

The volumes of the emulsion/water and emulsion/oil fronts (when theemulsion breaks) are thus recorded as a function of time in order toallow determination of the half life times of the water (T_(1/2 water))and of the oil (T_(1/2 oil)). The half life times are defined as thetimes from which half the volume of the phase considered has beenrecovered. Recovered is understood to mean non-emulsified.

The destabilization mechanisms observed can be described as follows:

In the initial state, i.e. at t=0, the emulsion is homogeneous, the oildroplets are homogeneously distributed within the aqueous continuousphase.

During a first stage, the phenomenon of oil droplets creaming isobserved, i.e. a water/emulsion front creates, separating two distinctphases: an aqueous phase at the bottom and the emulsion phase above.

During a second stage, the oil droplets creaming phenomenon clearlyslows down, and coalescence of the oil droplets is observed. A thirdphase therefore appears: the oil phase located above the emulsion.During this stage, the evolution rate of the oil/emulsion front isgenerally much higher than the evolution rate of the water/emulsionfront.

In the final state, total destabilization of the emulsion is observed.We therefore have a system only consisting of the two phases distributedaccording to their respective masses: the upper phase consisting of oiland the lower phase consisting of water.

Systems Tested

1) Surfactants

-   -   Dodecyltrimethyl ammonium bromide (DOTAB): cationic surfactant        having the general formula as follows:    -   Hexadecyltrimethyl ammonium bromide (CTAB): cationic surfactant        having the general formula as follows:    -   Sodium dodecyl sulfate (SDS): anionic surfactant having the        general formula as follows:        CH₃ ⁻(CH₂)₁₀ ⁻CH₂ ⁻O⁻SO₃—Na+

It can be noted that the surfactants used in the tests have rather highHLB values and preferably stabilize oil-in-water emulsions.

2) Polymers

-   -   Arabic gum extracted from acacia (molecular mass Mw of about        250,000 g/mol),    -   Acrylamide/Acrylamido methyl propane sulfonate copolymer AM/AMPS        having the general formula as follows:

One of the characteristics of the polymers is their viscosity at 10%active matter in water (Vis) expressed in centipoise (cP).AM/AMPS 80/20 x=20% and Vis=3300 cPAM/AMPS 90/10 x=10% and Vis=3000 cP.

-   -   Acrylamide/Acrylic acid copolymer of general formula as follows:

One of the characteristics of the polymers is their viscosity at 10%active matter in water (Vis) expressed in centipoise.AM/AA 90/10 x=10% and Vis=25000 cPAM/AA 90/10 x=10% and Vis=8000 cPAM/AA 90/10 x=10% and Vis=3500 cPAM/AA 80/20 x=20% and Vis=3600 cP.

-   -   Acrylamide/ADC copolymer of general formula as follows:

The AM/ADC 90/10 (x=10%) and AM/ADC 80/20 (x=20%) copolymers haveviscosities at 10% of the order of 3000 cP.

In the examples, the oil phase is either:

-   -   Colza methyl ester: Colza methyl ester (CME) is a methylated        colza oil derivative (T_(F)=−10° C., d₁₅=0.917-0.918)        or:    -   Dodecane: dodecane of purity 95% min. Containing at least 35%        n-dodecane. It is a colorless oil (Empirical formula:        C₁₂H₂₆M=170 g/mol; T_(F)=−9.9° C., T_(eb)=215-217° C.,        d₁₅=0.75).

Test No.1: Oil Phase: Colza Methyl Ester. Emulsifiers: DOTAB and ArabicGum (AG)

The operating conditions are as follows: Direct emulsion Emulsion typeCME in distilled water Oil/water proportions (%) 30/70 Volume prepared150 ml DOTAB brought into solution In distilled water Initial pH valueof the water pH = 8 Temperature Ambient Stirring type Heildoph/3-paddlepropeller Stirring rate 1000 rpm Stirring time 20 minutes

The results are as follows: T_(1/2) water (min) T_(1/2) ester (min)[DOTAB] Without Without (CMC = 15 mmol/l) AG 2 g/l AG AG 2 g/l AG Nosurfactant 0.6 1.1 0.6 1.3 2/1000 0.6 1.1 0.6 3.3 5/1000 0.6 22.7 0.6 >3days 1/100 0.6 33.2 0.6 >3 days 2/100 1.0 111.5 1.1 >3 days 1/10 24.1174.6 56.4 >3 days

The results show that the addition of anionic polymer (arabic gum AG) inthe presence of a cationic surfactant (DOTAB) leads to an emulsionstabilization. It can be noted that the surfactant alone, at aconcentration below {fraction (1/10)} of the CMC (critical micelleconcentration), cannot stabilize the emulsion (half life times below 2minutes). Addition of the anionic polymer allows to increase thestability very significantly. It can however be noted that a minimumsurfactant concentration is necessary, in this example, of {fraction(5/1000)} of the CMC.

It has also been observed that the arabic gum alone causes nosignificant stabilization of the colza methyl ester/water system. Infact, the half life times, in relation to an emulsion containing noadditive, are of the same order.

In all the tests hereafter, the operating conditions are as follows:Direct emulsion Emulsion type Dodecane in distilled water Oil/waterproportions (%) 40/60 Volume prepared 100 ml Surfactant and/or polymerbrought into In distilled water solution Initial pH value of the waterpH = 8 Temperature Ambient Stirring type Heildoph/3-paddle propellerStirring rate 800 rpm Stirring time 20 minutes

Test No.2: Oil Phase: Dodecane. Emulsifiers: DOTAB and AM/AA

The polymer is AM/AA (90/10, Vis=3500 cP) and the surfactant is DOTAB.The pH value is adjusted at 8, which ensures that at least part of theacrylic functions is in form of negatively charged acrylates.

The results are as follows: T1/2 water T1/2 dodecane (min) (min)Concentr. Without 1 g/l Without 1 g/l DOTAB (mmol/l) polymer polymerpolymer polymer No surfactant 0 <0.6 0.6 <0.6 0.6 2.5/100 CMC 0.375 <0.61.5 <0.6 5.5   5/100 CMC 0.75 <0.6 3.7 <0.6 15.8   1/10 CMC 1.5 <0.6 2.9<0.6 16.5   2/10 CMC 3 <0.6 2.8 <0.6 11.8   3/10 CMC 4.5 2.4 2.7 2.410.8

The presence of basic polymer leads to a notable stabilization of theemulsion, in particular for the T_(1/2) of the dodecane. Stabilizationis more marked for the DOTAB concentrations below {fraction (2/10)} ofthe CMC. In fact, under such conditions, an increase by more than 20times the T_(1/2) of the dodecane and about 5 times the T_(1/2) of thewater is observed.

Test No.3: Oil Phase: Dodecane. Emulsifiers: DOTAB and AM/AA. Influenceof the Polymer Concentration

In this test, the polymer used is AM/AA (90/10, Vis=3500 cP). The pHvalue is 7. The results are given in the table hereafter: [DOTAB] T1/2water T1/2 dodecane (mmol/l) (min) (min) No polymer 1.5 <0.6 <0.6 0.5g/l 1.5 1.40 8.6   1 g/l 1.5 2.9 16.5

These tests show that the polymer concentration is a parameter thatinfluences the emulsion stability. Thus, an increase in the polymerconcentration leads to a significant stabilization increase.

Test No.4: Oil Phase: Dodecane. Emulsifiers: DOTAB and AM/AA. Influenceof the Polymer Mass

In this part, the polymers used are the AM/AA 90/10 copolymers ofdifferent molecular masses (characterized by their viscosity at 10%).The polymer concentration is 1 g/l. The pH value is adjusted at 7.

The results are as follows: Polymer viscosity [DOTAB] T1/2 water T1/2dodecane (cP) (mmol/l) (min) (min) 25000 1.5 6.6 34.8 8000 1.5 4.60 15.62500 1.5 2.9 16.5

These examples show that the higher the molar mass of the polymer, thebetter the stabilization quality for the same concentration. In fact,this could be explained by the fact that the longer the chain, thegreater the steric hindrance at the interface, which consequently leadsto a greater stabilization effect. Furthermore, the polymers of highermass lead, at equal concentration, to a viscosity increase of theaqueous phase, which allows the creaming and coalescence phenomena toslow down.

Test No.5: Oil Phase: Dodecane. Emulsifiers: DOTAB and AM/AA. Influenceof the Polymer Charge Rate

In this test, the polymers used are AM/AA 90/10 (Vis=3500 cP) and AM/AA80/20 (Vis=3600 cP) at a concentration of 1 g/l. The pH value is 7.

The results are: [DOTAB] T1/2 water T1/2 dodecane Polymer (mmol/l) (min)(min) No polymer 1.5 <0.6 <0.6 AM/AA 90/10 1.5 2.9 16.5 AM/AA 80/20 1.514.4 254.3

It is clear that the charge rate of the polymer plays an important partin the stabilization efficiency of the emulsions. In fact, the massbeing equivalent, a polymer twice as charged allows to multiply by 15the half life times. This can be explained by the fact that the polymercontaining more charged monomers forms a more stable electrostaticcomplex with the surfactant molecules, considering the greater number ofinteractions of electrostatic type for the same chain length.

Test No.6: Oil Phase: Dodecane. Emulsifiers: DOTAB and AM/AA. Influenceof the Ionic Strength

In this example, the polymer used is AM/AA 80/20 (Vis=3600 cP) at aconcentration of 1 g/l at pH 7. The DOTAB concentration is 1.5 mmol/l.In order to study the influence of the ionic strength on the stabilityof an emulsion, sodium chloride is added to the aqueous phase for astudied concentration range between 0 and 1 mol/l.

The results are: [NaCl] T1/2 water T1/2 dodecane (mol/l) (min) (min)  014.4 254   10⁻⁴ 9.4 231   10⁻³ 6 156   10⁻² 3.8 66   10⁻¹ 3.2 8.9  1 12.7

The results show that the presence of sodium chloride in the continuousphase actually leads to a decrease in the emulsion stability. Thissensitivity to the ionic strength was expected because of the role ofthe electrostatic interactions on the formation of the interfacialcomplex. One may however consider that, for an ionic strength that isnot too high, the emulsion stability can be improved to a certain extentby increasing the surfactant concentration.

Test No.7: Oil Phase: Dodecane. Emulsifiers: DOTAB and AM/AMPS

The DOTAB concentration is 1.5 mmol/l. The tests were carried out withtwo pH values: 8 and 1. The polymer used is AM/AMPS (80/20). Thenegative charge is provided by the non pH-dependent SO₃-functions.

The results are: T1/2 water T1/2 dodecane (min) (min) pH = 8 Withoutpolymer <0.6 <0.6 AM/AMPS 80/20 15.5 158.5 1 g/l pH = 1 Without polymer<0.6 <0.6 AM/AMPS 80/20 4.4 96 1 g/l

The presence of this polymer also considerably increases the emulsionstability. One may assume that the slightly lower stabilization at pH=1,in relation to pH=8, can be due to the increase in the ionic strength ofthe medium by addition of HCl concentrated at 10 mol/l (about 0.5 ml in60 ml aqueous phase, i.e. a chloride concentration of 8.10⁻² mol/l) toobtain pH=1. This concentration is sufficient to generate a slightemulsion destabilization comparable to the previous example.

Test No.8: Oil Phase: Dodecane. Emulsifiers: DOTAB and AM/ADC

In this example, we examine the influence of the addition of a cationicpolymer of same charge as the DOTAB surfactant. The DOTAB concentrationis 1.5 mmol/l. The tests were carried out with two pH values: 8 and 1.The polymer used is AM/ADC (80/20). The positive charge is provided bythe quaternary amine functions of the non pH dependent ADC monomers.T1/2 water T1/2 dodecane pH = 8 (min) (min) Without polymer <0.6 <0.6AM/ADC 80/20 2 2.5 1 g/l

T1/2 water T1/2 dodecane pH = 1 (min) (min) Without polymer <0.6 <0.6AM/ADC 80/20 1.4 1.8 1 g/l

It is clear that the cationic polymer does not allow to significantlyimprove the emulsion stabilization in the presence of a cationicsurfactant, whether an acid or an alkaline medium. There is no formationof an interfacial polymer/surfactant complex. These results confirm therole of the attractions of electrostatic origin on the stabilization ofthe emulsion.

Test No.9: Oil Phase: Dodecane. Emulsifiers: SDS and AM/ADC

In the following tests, the surfactant is anionic: SDS.

In this test, the cationic polymer is AM/ADC 90/10 (Vis=3000 cP). Theresults are given in the following table: T1/2 water T1/2 dodecane Conc.Without 0.5 g/l Without 0.5 g/l SDS (mmol/l) polymer polymer polymerpolymer No 0 0.5 min 1 min 0.5 min 1 min surfactant   1/1000 0.006 0.5min 6 min 0.5 min 7 min 2.5/1000 0.015 0.5 min 6 min 0.5 min 5 h  5/1000 0.029 0.5 min 6 min 0.5 min >9 days

The presence of an oppositely charged polymer leads to an emulsionstabilization, in particular for the T1/2 of the dodecane. In relationto the system with DOTAB, stabilization is observed at an even lowerconcentration. From {fraction (5/1000)}^(th) of the CMC in SDS and 0.5g/l cationic polymer, a stabilization towards the coalescence of the oildroplets greater than one week is observed. The stabilizing effect isthus greatly marked, even for relatively low surfactant and polymerconcentrations.

Test No.10: Oil Phase: Dodecane. Emulsifiers: SDS and AM/ADC. Influenceof the Polymer Concentration

In this test, the cationic polymer is AM/ADC 90/10 (Vis=3000 cP). Theresults are given in the table hereunder: [SDS] Polymer T1/2 Xth CMCmmol/l g/l Water Dodecane 5/1000 0.03 1 8 min >15 days 5/1000 0.03 0.5 6min  >9 days 5/1000 0.03 0.25 4 min  9 days

The polymer concentration has an effect on the emulsion stability but asmall amount (0.25 g/l) is enough to stabilize the emulsion for morethan a week (concerning the T1/2 of the dodecane). This surfactant SDSand cationic polymer (ADC functions) mixture is therefore very efficientfor stabilization.

Test No.11: Oil Phase: Dodecane. Emulsifiers: SDS and AM/AMPS

In this test, the polymer (AM/AMPS 90/10) and the surfactant (SDS) areidentically charged. The results are given in the table hereunder: Conc.SDS (mmol/l) T1/2 water T1/2 dodecane No surfactant 0 5 min 5 min 5/10000.03 2 min 3 min

The anionic polymer does not allow to stabilize the emulsion in thepresence of an anionic surfactant.

1) An oil-in-water emulsion comprising at least a surfactant and ahydrosoluble polymer or copolymer, characterized in that said surfactantis oppositely charged in relation to said polymer or copolymer and inthat the surfactant is at a concentration below approximately 5.10⁻³mol/l. 2) An emulsion as claimed in claim 1, wherein the surfactant iscationic and the polymer is anionic. 3) An emulsion as claimed in claim1, wherein the surfactant is anionic and the polymer is cationic. 4) Anemulsion as claimed in claim 2, wherein the anionic polymer is anAM/AMPS type copolymer whose charged part proportion ranges between 1and 50%, preferably between 10 and 25%, and wherein the surfactant is ofDOTAB type. 5) An emulsion as claimed in claim 2, wherein the anionicpolymer is an AM/acrylic acid type copolymer used in basic pH whosecharged part proportion ranges between 1 and 50%, preferably between 10and 25%, and wherein the surfactant is of DOTAB type. 6) An emulsion asclaimed in claim 2, wherein the anionic polymer is a natural polymer,arabic gum for example. 7) An emulsion as claimed in claim 3, whereinthe cationic polymer is an AM/ADC type copolymer whose charged partproportion ranges between 1 and 50%, preferably between 10 and 25%, andwherein the surfactant is of SDS type. 8) A method of manufacturing anemulsion, from an aqueous continuous phase and an organic phase, of atleast one surfactant and at least one polymer or copolymer,characterized in that a surfactant and a hydrosoluble polymer orcopolymer, oppositely charged, are combined in the aqueous phase and inthat the polymer concentration is determined to obtain a stableoil-in-water emulsion with the lowest possible surfactant proportionbelow a 5.10⁻³ mol/l concentration. 9) A method as claimed in claim 8,wherein the polymer concentration is determined as a function of thecharge rate of the polymer and of the concentration of the surfactantused. 10) A method as claimed in claim 8, wherein the polymer andsurfactant concentrations are determined as a function of the ionicstrength of the medium.